1. Field of the Invention
The present invention relates to an abnormality detection apparatus for a battery pack including a plurality of unit batteries each of which is constituted by one, or adjacent two or more of battery cells, the apparatus being connected through detection lines to both electrodes of each of the unit batteries, and configured to detect a voltage across each of the unit batteries on the basis of voltages between each two adjacent detection lines.
2. Description of Related Art
FIG. 27 is diagram showing a part of an equivalent circuit of such an abnormality detection apparatus described in Japanese Patent No. 3603901. As shown in this figure, in this abnormality detection apparatus, an overcharge detecting circuit 110 and an overdischarge detecting circuit 120 are parallel-connected to each of battery cells Cn, C(n−1), C(n−2) constituting a battery pack. The overcharge detecting circuit 110 and the overdischarge detecting circuit 120 are respectively for determining whether or not the voltage across a corresponding battery cell is excessively high or excessively low. If the overcharge detecting circuit 110 detects an overcharge, the detection result is outputted to an OR circuit 132. On the other hand, if the overdischarge detecting circuit 120 detects an overdischarge, the detection result is outputted to an OR circuit 134. The outputs of the OR circuit 132 and the OR circuit 134 are logically combined by an OR circuit 136. By referring to the output of the output of the OR circuit 136, it is possible to determine presence of an overcharge condition or an overdischarge condition.
The above apparatus is provided with switching elements SWn, SW (n−1), SW (n−2). When one of these switching elements is turned on, both electrodes of a corresponding battery cell are short-circuited. In this state, if an overcharge or an overdischarge is detected, it can be determined that the detection line connected between the negative side electrode of the corresponding battery cell and a corresponding one of the overcharge detecting circuits 110 and the overdischarge detecting circuits 120 is broken. This determination is made on the basis of the fact that when the SWn, for example, is turned on, if the detection line Ln connected to the negative side electrode of the battery cell Cn is broken, the voltage of the detection line Ln is brought to the voltage of the detection line L(n+1) connected to the positive side electrode of the battery cell Cn.
However, the above conventional apparatus has a problem in that it is not possible to distinguish between breakage of the detection line and overcharge or overdischarge condition of the battery cell. Accordingly, when an abnormality is detected by this apparatus, it cannot be determined whether a part of the circuit structure of this apparatus should be replaced, or a battery pack should be replaced. Hence, there has been a problem that a normally operating battery pack is replaced unnecessarily, or a number of the detection lines are checked unnecessarily during a maintenance period.